Microevolutionary change might seem too unimportant to account for such amazing
evolutionary transitions as the origin of dinosaurs or the radiation of land
plants  however, it is not. Microevolution happens on a small time scale 
from one generation to the next. When such small changes build up over the course of
millions of years, they translate into evolution on a grand scale  in other
words, macroevolution!

The four basic evolutionary mechanisms  mutation, migration, genetic drift,
and natural selection  can produce major evolutionary change if given enough
time. And life on Earth has been accumulating small changes for 3.8 billion years
 more than enough time for these simple evolutionary processes to produce its
grand history.